A. Field of the Invention
The present invention relates to fluid valves, and in particular, to noise and cavitation control for ball-type fluid control valves.
B. Problems in the Art
The control of flow of gas and liquids under pressure generally requires some type of valve. There are a variety of types of these flow restriction devices. An example is what will be called a ball-type valve.
Ball-type valves are well known in the art. They can take many different forms. Some of the predominant types are called full-ball, restricted ball, and segmented ball valves.
In each instance, a flow path extends through a valve housing for the ball-type valve. A ball element (full, restricted, or segmented) is rotatable within the housing to block all, a portion, or essentially none of the flow path. As a result, fluid flow through the pathway and valve is controlled.
Ball-type valves are used in many applications. In certain applications, however, problems exist. One example is what will be called the noise problem. Particularly during the first fifty percent or so of opening of a ball valve, fluid stresses and fracture interaction from entering the restriction presented by the valve create acoustic energy or noise. In some instances this noise, if not controlled, is of such a level that it can cause physical damage to the valve and adjacent piping; as well as structures in the proximity of the valve. Moreover, noise of higher levels (for example, over 90 dB) can cause physical injury to humans. Additionally, government regulations cover some valve uses and require attenuation of noise below a certain level.
One attempt to control this noise utilizes essentially a muffler system. Noise is attempted to be muffled in the sense of isolating and insulating the valve, or by placing mufflers down stream from the valve in the fluid flow line. These type of devices are relatively costly and can take up substantial amounts of space.
Other attempts have utilized what will be called baffles or inserts into the ball valve itself. Examples of these type of devices can be seen in the following patents: T1 -Patent No.? Inventor? Issue Date? -4,212,321 Hulsey Jul. 15, 1980 - 4,364,415 Polon Dec. 21, 1982 - 4,479,510 Bey Oct. 30, 1984 - 4,530,375 Bey Jul. 23, 1985 - 4,540,025 Ledeen et al. Sep. 10, 1985 - 4,610,273 Bey Sep. 9, 1986 - 4,889,163 Engelbertsson Dec. 26, 1989 - 5,070,909 Davenport Dec. 10, 1991 - 1,128,489 Canadian Patent - 0,123,408 European Patent -
These attempts at noise reduction or attenuation have certain deficiencies. First, they have limited impact on noise reduction. Many also severely restrict fluid flow or adversely effect flow characteristics of the valve. Structural soundness, strength, and durability problems can also exist.
A second problem with ball-type valves is the potential for incipient cavitation or turbulence. Such cavitation occurs in ball-like valves at relatively low opening positions (generally less than 50 percent) as a result of flow separation occurring caused by the high velocity of liquid past the leading edge of the flow pathway bore through the ball trim element. If such flow separation occurs, vapor bubbles form. Cavitation can be severe enough that it physically damages the valve. For reasons similar to the noise problem, attempted solutions to cavitation problems have not been entirely satisfactory.
It is important to emphasize that any attempts to control noise or cavitation which effect the flow characteristic of the valve can be troublesome. It is generally desired, if not required, that a monotonic relationship exist between the percentage of valve opening and the percentage of maximum flow through the valve. In other words, for each incremental increase or decrease in opening of the valve, it is generally desired that there be an increase or decrease in flow capability through the valve.
It is obvious that if a noise or cavitation control device severely restricts flow or presents an undesirable flow characteristic for the valve, that the utility of the valve may be severely diminished. It is therefore important, and a problem in the art, to achieve required flow and maintain the desired flow characteristics when attempting to attenuate and control noise and cavitation.
It is therefore a primary object of the present invention to provide a noise and cavitation control ball-type valve trim element which improves over the state of the art.
It is an object of the invention to provide a trim element as above described which can be used in a variety of ball-type valves where noise or cavitation can be a problem.
Another object of the invention is to provide a trim element as above described which efficiently and economically provides acceptable noise levels.
A still further object of the invention is to provide a trim element as above described which provides acceptable noise levels while maintaining desired flow characteristics through the valve.
A still further object of the invention is to provide a trim element as above described which is effective in dealing with situations where cavitation is a problem while maintaining desired flow characteristics for the valve.
Another object of the present invention is to provide a trim element as above described which has a non-complex structure that can be used to solve, diminish, or reduce complex noise or cavitation problems.
Another object of the present invention is to provide a trim element as above described which is economical to manufacture and install, and is durable and easy to maintain.
Another object of the present invention is to provide a trim element as above described which allows operation of ball-type valves at higher differential pressures with minimum potential of cavitation damage.
A still further object of the invention is to provide a trim element as above described which minimizes adverse effect on flow capacity or characteristic of the valve.
These and other objects, features, and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.